pstore/ramoops: Fix typo as there is no "reserver"

For some reason my finger always hits the 'r' after typing "reserve".
Fix the typo in the Documentation example.

Fixes: d9d814eebb1ae ("pstore/ramoops: Add ramoops.mem_name= command line option")
Signed-off-by: Steven Rostedt (Google) <[e-mail]>
Acked-by: Mike Rapoport (Microsoft) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Kees Cook <[e-mail]>

Documentation/admin-guide/ramoops.rst

···
     takes a size, alignment and name as arguments. The name is used
     to map the memory to a label that can be retrieved by ramoops.
 
-	reserver_mem=2M:4096:oops  ramoops.mem_name=oops
+	reserve_mem=2M:4096:oops  ramoops.mem_name=oops
 
 You can specify either RAM memory or peripheral devices' memory. However, when
 specifying RAM, be sure to reserve the memory by issuing memblock_reserve()