usb: gadget: function: f_sourcesink: fix sparse warning

this patch fixes following sparse warnings:

f_sourcesink.c:347:34: warning: symbol 'ss_int_source_comp_desc' was not declared. Should it be static?
f_sourcesink.c:365:34: warning: symbol 'ss_int_sink_comp_desc' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>