package/ripgrep: fix build directories

RIPGREP_CARGO_MODE was no longer defined after 832c076f26 and caused
issues during the install step as the build directory was malformed.

This patch maintains the release/dev profile distinction, while also
assigning appropriate build folders.

Fixes:
 - http://autobuild.buildroot.net/results/a4cd7ecc6d983aa6f15d3be1e21529f17e04b825/
 - http://autobuild.buildroot.net/results/2bab8ffa590d4c4eabffe94ed27311c7f6607c98/



Signed-off-by: Sam Voss <sam.voss@gmail.com>
CC: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>