libv4l: fix a typo to not override the LIBV4L_DEPENDENCIES variable

Otherwise host-pkgconf will not be installed and the configure script
will fail with an error like this one:

./configure: line 16346: PKG_PROG_PKG_CONFIG: command not found
[snip]
./configure: line 20511: syntax error near unexpected token `X11,'
./configure: line 20511: `PKG_CHECK_MODULES(X11, x11, x11_pkgconfig=yes,
x11_pkgconfig=no)'

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Tested-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>