staging/easycap: wait_i2c should be static

wait_i2c is only used from easycap_low.c
so remove it from the easycap.h and mark it static

Cc: Mike Thomas <rmthomas@sciolus.org>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>