perl: do_create_rdepends_inc override syntax

The do_create_rdepends_inc function is used to recreate
the perl-rdepends.txt file. Update RDEPENDS_ to RDEPENDS:
for the new override syntax.

Signed-off-by: Tim Orling <timothy.t.orling@intel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>