kernel-module-split.bbclass: Fix modinfo decoding in old kernels

kernel-module-split.bbclass: Fix modinfo decoding in old kernels

Before linux commit d36b691077dc59c74efec0d54ed21b86f7a2a21a, some
strings contained invalid utf-8 character which made
split_kernel_module_packages unhappy when parsing ums-isd200.ko:

Exception: UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf6 in position 21: invalid start byte

(From OE-Core rev: 503b977acf6984120818cbc5cfd35ff2cffb39cd)

Signed-off-by: Pau Espin Pedrol <pespin@sysmocom.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>