HID: amd_sfh: change global variables to static

Smatch reports this representative issue
amd_sfh_hid_report_desc.h:182:10: warning: symbol 'gyro3_report_descriptor' was not declared. Should it be static?
Similar issues for comp3_report_descriptor and als_report_descriptor.

Global variables should not be defined in header files.
This only works because amd_sfh_hid_report_desc.h in only included by
amd_sfh_hid_desc.c so change the storage-class specifiers to static.

Signed-off-by: Tom Rix <trix@redhat.com>
Acked-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>