ANDROID: firmware_loader: Fix warning with firmware_param_path_set

Compile time warning is observed with firmware_param_path_set()
for using the __setup() macro when firmware_loader enabled as module.

drivers/base/firmware_loader/main.c:428:19: warning: 'firmware_param_path_set'
defined but not used [-Wunused-function]

Fix the above warning by using the module_param_cb instead of __setup for
firmware_class.path commandline.

Bug: 202192667
Fixes: d551647f ("ANDROID: firmware_loader: Add support for customer firmware paths")
Change-Id: I73cdee9815e84a507ac886e6e181d4a489fd2e5f
Signed-off-by: Prasad Sodagudi <quic_psodagud@quicinc.com>