halapi: Remove build warning due to misused 'const' keyword

halapi: Remove build warning due to misused 'const' keyword

Remove the following build warning due to misused 'const' keyword.

[Build warning message]
[ 11%] Building C object CMakeFiles/hal-api-common.dir/src/hal-api-common.c.o
[ 22%] Building C object CMakeFiles/hal-api-common.dir/src/hal-api-conf.c.o
/home/abuild/rpmbuild/BUILD/hal-api-common-0.0.1/src/hal-api-common.c:
		In function '__get_backend_library_data':
/home/abuild/rpmbuild/BUILD/hal-api-common-0.0.1/src/hal-api-common.c:684:9:
		warning: passing argument 1 of 'g_free' discards 'const' qualifier
		from pointer target type [-Wdiscarded-qualifiers]
  684 |  g_free(backend_module_name);

Change-Id: I8576581f3a40d140293fbbc62433107a25a9998b
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>