mtd: fix build against recent uClibc 0.9.33

Commit fae7cc33 added a local rpmatch() implementation. However, the
rpmatch() implementation was backported to the 0.9.33 branch, thus breaking
the Buildroot default toolchain. Rename the local rpmatch() to avoid
collision.

Fixes:
http://autobuild.buildroot.net/results/51f/51fe39bd942e4d8d0045ac810708719b9459e21f/



Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>