doc: dfu: fix typos in README.dfu

Fix some typos.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Lukasz Majewski <lukma@denx.de>
diff --git a/doc/README.dfu b/doc/README.dfu
index 29230ec..4b9f883 100644
--- a/doc/README.dfu
+++ b/doc/README.dfu
@@ -48,12 +48,12 @@
   CONFIG_CMD_DFU
 
 Environment variables:
-  the dfu command use 3 environments variables:
+  the dfu command uses 3 environments variables:
   "dfu_alt_info" : the DFU setting for the USB download gadget with a semicolon
                    separated string of information on each alternate:
                    dfu_alt_info="<alt1>;<alt2>;....;<altN>"
 
-                   when only several device are used, the format is:
+                   when several devices are used, the format is:
                    - <interface> <dev>'='alternate list (';' separated)
                    - each interface is separated by '&'
                 dfu_alt_info=\
@@ -63,7 +63,7 @@
                    "<interfaceI> <devI>=<altY+1>;....;<altZ>&"
 
   "dfu_bufsiz" : size of the DFU buffer, when absent, use
-                 CONFIG_SYS_DFU_DATA_BUF_SIZE (8MiB by default)
+                 CONFIG_SYS_DFU_DATA_BUF_SIZE (8 MiB by default)
 
   "dfu_hash_algo" : name of the hash algorithm to use