package/libdrm: fix meson build option spelling

The "manpages" option should be "man-pages", otherwise Meson will abort
configuring the build due to the attempt of using an invalid option.

Signed-off-by: Adrian Perez de Castro <aperez@igalia.com>

Author: aperezdc

package/libdrm/libdrm.mk

@@ -16,7 +16,7 @@ LIBDRM_DEPENDENCIES = \
 
 LIBDRM_CONF_OPTS = \
 	-Dcairo-tests=false \
-	-Dmanpages=false
+	-Dman-pages=false
 
 ifeq ($(BR2_PACKAGE_LIBATOMIC_OPS),y)
 LIBDRM_DEPENDENCIES += libatomic_ops