kernel: use .patch extension for all patches

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

diff --git a/target/linux/gemini/patches-4.4/060-cache-fa.diff b/target/linux/gemini/patches-4.4/060-cache-fa.patch
similarity index 100%
rename from target/linux/gemini/patches-4.4/060-cache-fa.diff
rename to target/linux/gemini/patches-4.4/060-cache-fa.patch

diff --git a/target/linux/generic/patches-3.18/091-mtd-spi-nor-add-support-Spansion_S25FL164K b/target/linux/generic/patches-3.18/091-mtd-spi-nor-add-support-Spansion_S25FL164K.patch
similarity index 100%
rename from target/linux/generic/patches-3.18/091-mtd-spi-nor-add-support-Spansion_S25FL164K
rename to target/linux/generic/patches-3.18/091-mtd-spi-nor-add-support-Spansion_S25FL164K.patch