x86/mtrr: Convert to use match_string() helper

The helper returns index of the matching string in an array.
Replace the open coded array lookup with match_string().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Link: http://lkml.kernel.org/r/20180515175759.89315-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/mtrr/if.c

@@ -149,17 +149,16 @@ mtrr_write(struct file *file, const char __user *buf, size_t len, loff_t * ppos)
 		return -EINVAL;
 	ptr = skip_spaces(ptr + 5);
 
-	for (i = 0; i < MTRR_NUM_TYPES; ++i) {
-		if (strcmp(ptr, mtrr_strings[i]))
-			continue;
-		base >>= PAGE_SHIFT;
-		size >>= PAGE_SHIFT;
-		err = mtrr_add_page((unsigned long)base, (unsigned long)size, i, true);
-		if (err < 0)
-			return err;
-		return len;
-	}
-	return -EINVAL;
+	i = match_string(mtrr_strings, MTRR_NUM_TYPES, ptr);
+	if (i < 0)
+		return i;
+
+	base >>= PAGE_SHIFT;
+	size >>= PAGE_SHIFT;
+	err = mtrr_add_page((unsigned long)base, (unsigned long)size, i, true);
+	if (err < 0)
+		return err;
+	return len;
 }
 
 static long