package/grpc: fix legal info

Commit 0fc2438ff6e3d14cc9e7b546e2909e386db33439 forgot to update hash of
LICENSE (full text of MPLv2 included with
https://github.com/grpc/grpc/commit/05fcd826f477ef1a024a2defa5e4b3d78f5e6eb4)

Fixes:
 - http://autobuild.buildroot.org/results/98b820f85cd32596bde6bbee2cfc7e07ecfa454b

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/grpc/grpc.hash

@@ -1,3 +1,3 @@
 # Locally computed
 sha256  9b1f348b15a7637f5191e4e673194549384f2eccf01fcef7cc1515864d71b424  grpc-1.48.0.tar.gz
-sha256  277adcc1dcef8359b1efb48e628635f88b40be8fbd64e82fd0169930d135d7a5  LICENSE
+sha256  590198e3f305f2c347fde64d637c65492bbef554db6c8364e149cd375e3797ee  LICENSE