MIPS: Avoid buffer overrun in mips_cm_error_report

Commit 3885c2b463f6 ("MIPS: CM: Add support for reporting CM cache
errors") added cases for decoding errors reported by CM3, but leaves the
buf variable which is printed as a string uninitialised for cause values
other than 1, 2 or 3. Fix by ensuring the buf variable is initialised to
an empty string in such cases.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11187/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/mips-cm.c

@@ -366,6 +366,8 @@ void mips_cm_error_report(void)
 				 cm3_cmd_group[cmd_group_bits],
 				 cm3_cca_bits, 1 << mcp_bits,
 				 cm3_tr[cm3_tr_bits], sched_bit);
+		} else {
+			buf[0] = 0;
 		}
 
 		pr_err("CM_ERROR=%llx %s <%s>\n", cm_error,