meson: don't escape module_foo in kmod.pc

meson: don't escape module_foo in kmod.pc

The kmod.pc file, contains module_signatures and module_compressions
space-separated lists, indicating how kmod is built. For the meson
generated file, any spaces are escaped where the autotools one does not
do that.

Update the meson build to be consistent with the original autotools one
and omit the escaping that we don't want.

Aside: seems like autotools does not escape the directory variables
either, so if the path(s) have any spaces in them pkg-config (pkgconf at
least) produces rubbish, quite rightfully IMHO.

Eg.
  $ cat .../autotools-file.pc
  prefix=/usr
  includedir=${prefix}/include bar
  Cflags: -I${includedir}
  ...
  $ pkg-config --cflags autotools-file.pc
  bar

  $ cat .../meson-file.pc
  prefix=/usr
  includedir=${prefix}/include\ bar
  Cflags: -I${includedir}
  ...
  $ pkg-config --cflags meson-file.pc
  -I/usr/include\ bar

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/217
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>