Documentation/admin-guide: kernel-parameters: fix "io7" parameter description

Fix punctuation and capitalization for the "io7" boot parameter.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Link: https://lore.kernel.org/r/20200918054751.6538-1-rdunlap@infradead.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-parameters.txt

@@ -1959,7 +1959,7 @@
 			1 - Bypass the IOMMU for DMA.
 			unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
 
-	io7=		[HW] IO7 for Marvel based alpha systems
+	io7=		[HW] IO7 for Marvel-based Alpha systems
 			See comment before marvel_specify_io7 in
 			arch/alpha/kernel/core_marvel.c.