MAINTAINERS: Update platform-drivers-x86 maintainer and tree

Update the general entry for drivers/platform/x86 with myself as
maintainer and point to my tree.

Leave Matthew Garrett as maintainer of the two drivers called out
specifically elsewhere in MAINTAINERS.
Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>

MAINTAINERS

@@ -10057,9 +10057,9 @@ F:	Documentation/x86/
 F:	arch/x86/
 
 X86 PLATFORM DRIVERS
-M:	Matthew Garrett <matthew.garrett@nebula.com>
+M:	Darren Hart <dvhart@infradead.org>
 L:	platform-driver-x86@vger.kernel.org
-T:	git git://cavan.codon.org.uk/platform-drivers-x86.git
+T:	git git://git.infradead.org/users/dvhart/linux-platform-drivers-x86.git
 S:	Maintained
 F:	drivers/platform/x86/