kconfig: mconf: fix HOSTCC call

Commit c0f975af ("kconfig: Support building mconf with vendor
sysroot ncurses") introduces a bug when HOSTCC contains parameters:
the whole command line is treated as the program name (with spaces
in it). Therefore, we have to remove the quotes.

Fixes: c0f975af ("kconfig: Support building mconf with vendor sysroot ncurses")
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>